Discontinuous Reception (DRX) is the periodic switching off of a receiver, usually to save energy. DRX cycles can be configured in the LTE downlink so that user equipment (UE) does not have to decode the Physical Downlink Control CHannel (PDCCH) or receive Physical Downlink Shared CHannel (PDSCH) transmissions in certain subframes. UE in a cell forward access channel (Cell_FACH) may implement discontinuous reception (DRX) when receiving data from a radio network controller (RNC) via a high speed downlink shared channel (HS-DSCH). See, e.g., 3GPP TS36.321 Section 5.7 for connected mode, and TS36.304 Section 7.1 for idle mode.
Generally speaking, each of a sequence of core network (CN) broadcast periods has associated with it a respective DRX schedule period during which a scheduling message (SM) may be transmitted by the RNC to the UE to schedule thereby transmission of cell broadcast (CB) messages from the RNC to the UE during a DRX schedule period of an upcoming CN broadcast period. The SM typically occupies a fixed number (e.g., 40) of Common Traffic Channel (CTCH) block sets within the DRX schedule period.